Resonance Structures

Definition

Resonance structures are a set of contributing structures that describe the delocalization of electrons in a molecule. They represent the different ways in which the atoms in a molecule can be bonded to satisfy the octet rule and create the most stable arrangement of electrons.

5 Must Know Facts For Your Next Test

1. Resonance structures are used to describe the bonding in molecules with delocalized electrons, such as those with conjugated systems.
2. The more resonance structures that can be drawn for a molecule, the more stable the molecule is, as the electrons are more delocalized.
3. Curved arrows are used to show the movement of electrons during the formation of resonance structures.
4. Resonance structures are important in understanding the reactivity and stability of organic compounds, including alkynes, aromatic compounds, and carboxylic acids.
5. The formal charge of an atom in a resonance structure can help determine the most stable arrangement of electrons in a molecule.

Review Questions

• Explain how resonance structures are used in drawing chemical structures (1.12) and how they contribute to the stability of a molecule.
  • Resonance structures are used in drawing chemical structures to depict the delocalization of electrons within a molecule. By drawing multiple contributing structures that satisfy the octet rule, the true structure of the molecule can be represented as a resonance hybrid - a weighted average of these resonance forms. The more resonance structures that can be drawn for a molecule, the more stable the molecule is, as the electrons are more evenly distributed and delocalized, lowering the overall energy of the system.
• Describe the role of resonance structures in understanding polar reaction mechanisms (6.5) and the acidity of alkynes (9.7).
  • Resonance structures are crucial for understanding polar reaction mechanisms, as the movement of electrons during the mechanism can be depicted using curved arrows. This allows for the identification of partial charges and the most reactive sites in the molecule. In the case of alkyne acidity (9.7), resonance structures help explain the formation of acetylide anions. The delocalization of electrons in the conjugated system of the alkyne stabilizes the resulting negatively charged acetylide ion, making it a stronger base.
• Analyze how resonance structures contribute to the stability of conjugated dienes (14.1), aromatic heterocycles (15.5), and the oxidation of aromatic compounds (16.8).
  • Resonance structures are fundamental to understanding the stability of conjugated systems, such as conjugated dienes (14.1) and aromatic heterocycles (15.5). The delocalization of electrons across multiple p-orbitals in these systems leads to increased stabilization, as evidenced by the high degree of resonance that can be drawn. This stabilization also affects the reactivity of these compounds, as seen in the oxidation of aromatic compounds (16.8), where the aromatic resonance structures help to explain the relative stability and reactivity of the products.

Related terms

Resonance Hybrid: The actual structure of a molecule that is best described by a weighted average of its resonance structures, rather than any single contributing structure.

Conjugation: The overlap of p-orbitals in adjacent multiple bonds or lone pairs, which allows for the delocalization of electrons and the formation of resonance structures.

Formal Charge: The charge assigned to an atom in a molecule, calculated by subtracting the number of nonbonding electrons and half the number of bonding electrons from the atom's atomic number.